实践：在模型空间下的法线纹理映射

最近看《Unity Shader入门精要》这本书，看到第七章的时候，作者分别实现了在切线空间和世界空间下的法线纹理映射，其中提到也可以在其他空间实现，于是来实践一下在模型空间的实现，代码如下：

Shader "Chapter7/NormalMapObjectSpace"
{
    Properties
    {
        _Color("Color Tint", Color) = (1, 1, 1, 1)
        _MainTex("Main Tex", 2D) = "white" {}
        _BumpMap("Normal Map", 2D) = "bump" {}
        _BumpScale("Bump Scale", Float) = 1.0
        _Specular("Specular", Color) = (1, 1, 1, 1)
        _Gloss("Gloss", Range(8.0, 256)) = 20
    }
    SubShader
    {
        Pass
        {
            Tags{"LightMode" = "ForwardBase"}
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Lighting.cginc"
            
            fixed4 _Color;
            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _BumpMap;
            float4 _BumpMap_ST;
            float _BumpScale;
            fixed4 _Specular;
            float _Gloss;

            struct a2v
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float4 tangent : TANGENT;
                float4 texcoord : TEXCOORD0;
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                float4 uv : TEXCOORD0;
                float4 TtoW0 : TEXCOORD1;
                float4 TtoW1 : TEXCOORD2;
                float4 TtoW2 : TEXCOORD3;
                float3 lightDir : TEXCOORD4;
                float3 viewDir : TEXCOORD5;
            };

            v2f vert (a2v v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv.xy = v.texcoord.xy * _MainTex_ST.xy + _MainTex_ST.zw;
                o.uv.zw = v.texcoord.xy * _BumpMap_ST.xy + _BumpMap_ST.zw;

                float3 objPos = v.vertex.xyz;
                fixed3 objNormal = v.normal;
                fixed3 objTangent = v.tangent.xyz;
                fixed3 objBinormal = cross(objNormal, objTangent) * v.tangent.w;

                o.TtoW0 = float4(objTangent.x, objBinormal.x, objNormal.x, objPos.x);
                o.TtoW1 = float4(objTangent.y, objBinormal.y, objNormal.y, objPos.y);
                o.TtoW2 = float4(objTangent.z, objBinormal.z, objNormal.z, objPos.z);

                o.lightDir = ObjSpaceLightDir(v.vertex).xyz;
                o.viewDir = ObjSpaceViewDir(v.vertex).xyz;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                float3 objPos = float3(i.TtoW0.w, i.TtoW1.w, i.TtoW2.w);
                fixed3 lightDir = normalize(i.lightDir);
                fixed3 viewDir = normalize(i.viewDir);

                fixed3 bump = UnpackNormal(tex2D(_BumpMap, i.uv.zw));
                bump.xy *= _BumpScale;
                bump.z = sqrt(1.0 - saturate(dot(bump.xy, bump.xy)));
                bump = normalize(half3(dot(i.TtoW0.xyz, bump), dot(i.TtoW1.xyz, bump), dot(i.TtoW2.xyz, bump)));

                fixed3 albedo = tex2D(_MainTex, i.uv).rgb * _Color.rgb;
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz * albedo;
                fixed3 diffuse = _LightColor0.rgb * albedo * max(0, dot(bump, lightDir));
                fixed3 halfDir = normalize(lightDir + viewDir);
                fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(max(0, dot(bump, halfDir)), _Gloss);
                fixed3 color = ambient + diffuse + specular;
                return fixed4(color, 1);
            }
            ENDCG
        }
    }
    FallBack"Specular"
}

总体写法基本参考的是世界空间的写法，只不过坐标，法线，切线，光线角度，观察角度都是用的模型参数，最终呈现的效果也和其他两个空间一样，记录一下。